Vinculin is an essential cytoskeletal protein that acts as a scaffold to link transmembrane receptors to actin filaments, thereby playing a crucial role in cell adhesion, motility, and force transmission between cells. While vinculin is ubiquitously expressed, metavinculin, a larger isoform of vinculin, is selectively expressed in smooth and cardiac muscle cells. Similar to vinculin, metavinculin can directly associate with actin and remodel the actin cytoskeleton. However, distinct from vinculin, metavinculin contains an additional exon which encodes a 68-residue insert. Point mutations in the 68-residue insert have been associated with altered actin organization and heart disease, notably dilated cardiomyopathy (DCM) and hypertrophic cardiomyopathy (HCM). Both DCM and HCM are diseases of myocardium, or the heart muscle, that prevent the heart from pumping blood normally because of disruption in force transmission. Metavinculin expression is higher in muscle cells that require greater force transmission. Given the link between metavinculin expression and force transmission, including its role in actin cytoskeleton organization, it is likly that metavinculin plays an important role in force generation and transmission through its interaction with the actin cytoskeleton. Yet, a comprehensive and complete study to examine how metavinculin binds and remodels actin has not been conducted. Therefore, the overall objective will be to characterize metavinculin interactions with actin and the role of this interaction in force transmission between cells using methods such as actin cosedimentation assay, negative-stain electron microscopy (EM), cryo-EM, and fluorescence microscopy. In aim 1, I will characterize the actin filament binding and remodeling properties of metavinculin and associated disease mutants. In aim 2, I will determine whether the presence of vinculin, at different metavinculin to vinculin ratios, directly modulates the ability of wild-type metavinculin and metavinculin disease mutants to regulate actin filament organization. In aim 3, I will examine the mechanotransduction properties of wild-type and disease mutant metavinculin in vascular smooth muscle cells. These studies will provide the fundamental information necessary for determining the role that metavinculin plays in actin reorganization and ultimately in force transduction properties, providing groundwork for how metavinculin disease mutants contribute to associated cardiac myopathies.